WO1995009443A1 - Process for producing luminescent elemental structures - Google Patents

Process for producing luminescent elemental structures Download PDF

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Publication number
WO1995009443A1
WO1995009443A1 PCT/DE1994/001168 DE9401168W WO9509443A1 WO 1995009443 A1 WO1995009443 A1 WO 1995009443A1 DE 9401168 W DE9401168 W DE 9401168W WO 9509443 A1 WO9509443 A1 WO 9509443A1
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Prior art keywords
layer
microcrystalline
layers
produced
hydrogen
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PCT/DE1994/001168
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German (de)
French (fr)
Inventor
Reinhard Schwarz
Svetoslav Koynov
Thomas Fischer
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Reinhard Schwarz
Svetoslav Koynov
Thomas Fischer
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Priority claimed from DE4333416A external-priority patent/DE4333416C2/en
Application filed by Reinhard Schwarz, Svetoslav Koynov, Thomas Fischer filed Critical Reinhard Schwarz
Publication of WO1995009443A1 publication Critical patent/WO1995009443A1/en

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    • H01L33/26—Materials of the light emitting region
    • H01L33/34—Materials of the light emitting region containing only elements of Group IV of the Periodic Table
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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Definitions

  • the invention relates to a method for producing luminescent element structures by means of the CVD method, wherein microcrystalline layers of elements of the IV. HGr are deposited and these are passivated in situ.
  • Luminescence is the emission of light in the visible range, in the UV and IR spectral range, including from solids after the supply of energy.
  • the luminescence is due to a transition from an electron from an energetically higher state to an unoccupied energetically lower state. Since unoccupied electron states are often treated as positively charged "holes", luminescence can also be described as a recombination of an electron hole pair in which the energy released is released is at least partially emitted in the form of a light quantum (photon).
  • the luminescence processes can be divided into photoluminescence (optical excitation) and electroluminescence (electrical excitation by applying a voltage) according to the type of energy supply.
  • the phenomenon of luminescence is of particular interest in the semiconducting materials, since it enables various applications in microelectronics.
  • Typical materials with such a direct band transition are, for example, GaAs compound semiconductors.
  • silicon is a semiconductor material with an indirect band transition. It was therefore to be expected that silicon would not be available for electroluminescence applications.
  • various methods and processes have recently become known which make it possible to produce an electroluminescent Si structure.
  • microcrystalline layers on a substrate by means of the CVD method and at the same time to passivate these microcrystalline layers in situ.
  • Layers (activated layer - AL) must not exceed a thickness of 100 A. It is preferred here if the AL is in the range from 20 to 50 ⁇ .
  • microcrystalline layers themselves can be controlled with respect to their crystallite content by generating the microcrystalline layers using the CVD method.
  • microcrystalline layers are deposited using the CVD method. From the literature are here for the production of microcrystalline silicon layers known various processes.
  • the layers are produced using SiH 4 in hydrogen as the process gas.
  • SiH 4 is used in a highly dilute form in hydrogen (less than 5% by volume) (T. Hamasaki, H. Kurata, M. Hirose, U. Osaka, Appl. Phys. Lett. 37 (1980) 1084).
  • the low-temperature formation of the crystalline phase can be understood as an equilibrium between the silicon deposition and the removal of the areas with disordered Si-Si bonds by the atomic hydrogen. This process is referred to as hydrogen etching (CC Tsai, GB Anderson, R. Thompson, B. Wacker, J. Non-Cryst. Sol. 114 (1989) 151).
  • Step for example, deposited an amorphous SiH layer under the conditions favorable for the Si deposition and then, in a second step, carried out the hydrogen etching under the conditions required for the hydrogen etching (A. Asano, T. Ichimura, H. Sakai, J. Appl. Phys. 65 (1989) 2439. A. Asano, Appl. Phys. Lett. 56 (1990) 533).
  • the hydrogen treatment is carried out in such a way that a constant hydrogen flow is conducted into the CVD reactor over the substrate.
  • microcrystalline layers are also possible by means of a so-called CC-CVD process (closed chamber CVD process).
  • CC-CVD process closed chamber CVD process
  • This deposition method corresponds essentially to that described above, but with the difference that the hydrogen treatment is carried out in a closed system, in which case significantly higher deposition rates are achieved.
  • the microcrystalline layers produced in this way are particularly distinguished by the fact that the microcrystalline layer has a crystallite content of 20 to 95%, among other things also so-called element dots, i.e. spatially limited crystallites.
  • the hydrogen treatment is carried out in such a way that after the deposition of the amorphous layer with process gases known per se and under usual conditions, the process gas flow and the hydrogen flow and the connection of the CVD reactor to the pump are interrupted at least temporarily.
  • the hydrogen treatment is carried out with the amount of hydrogen still in the reactor.
  • the procedure is preferably such that the hydrogen flow is switched off with a time delay, so that there is an increased proportion of hydrogen in the reactor. Because the hydrogen is present in the closed system, the conversion of the amorphous
  • the silicon atoms are etched away from the amorphous solid silicon phase by the hydrogen atoms, and an SiH plasma is formed. Since the attack of the hydrogen atoms takes place at preferred locations on the amorphous silicon layer, corresponding microcrystalline layers also form at preferred locations.
  • Working in a closed system ensures that the SiH x gas species that form in the reactor are not removed from the system by the continuous flow of hydrogen, but that a quasi-steady state is achieved, so that an increased deposition rate is achieved can. It is therefore preferably proposed that the proportion of hydrogen be increased so that the etching is accelerated and a further significantly increased deposition rate is achieved. This is achieved in that the process gas stream and the hydrogen stream and the
  • the process offers the further advantage that the crystallite content can be controlled individually by the duration of the hydrogen treatment.
  • the crystallite content that can be achieved with the method according to the invention is at a maximum at 95%.
  • the crystallite size can also be set by selecting the process parameters.
  • the process described above is called the CC-CVD process.
  • the cyclic CC-CVD process therefore consists of a repeatable cycle, each cycle consisting of two steps, namely a) the deposition of a thin amorphous silicon layer and
  • An advantage of the method according to the invention is that several cycles can be carried out in succession in one process. Depending on the desired layer thickness, 2 to 2000 cycles can thus be carried out, so that a corresponding layer can be realized.
  • the method presented can basically be carried out with all common CVD methods. These include ECR-CVD, VHF-CVD and hot wire CVD processes. It is also possible to use different CVD processes for the individual steps of each cycle.
  • the method according to the invention is carried out with silicon as element and SiH 4 and hydrogen as process gases. It is essential to the invention in the proposed method that after the production of the microcrystalline layer, as described above, this microcrystalline layer is passivated in situ either in the open or in the closed CVD process. Two variants are proposed for this.
  • the passivation can be carried out using oxidizing and / or nitriding gases, such as, for example, plasma-activated N 2 O or oxygen, on the other hand the passivation can also be carried out by depositing a passivation layer.
  • the passivation layer has a thickness of 10 to 100 ⁇ and preferably consists of SiO x or SiN x .
  • the passivation is carried out in situ, ie in the CVD system, directly after the layer has been deposited. This enables a particularly simple and inexpensive procedure for producing the luminescent element structures. Both the deposition and the passivation are therefore possible with a CVD system in one process step.
  • a so-called activated layer is formed according to the invention by depositing a microcrystalline layer and subsequent passivation.
  • this AL does not consist of a passivated layer, but of 2 to 2,000, preferably up to 200, microcrystalline and passivated layers deposited on top of one another.
  • AI is understood to mean both a single microcrystalline layer that is passivated and 2 to 2,000 microcrystalline and passivated layers deposited one above the other, which then together form the AL.
  • the invention naturally also includes AL layers which consist of 2 to 2,000 microcrystalline layers arranged next to one another, each layer does not necessarily have to be passivated. For example, only every second layer can be passivated without any relevant impairment of the luminescence.
  • the method according to the invention offers further advantages. It is not only possible to use the CVD process to produce an AL consisting of 2 to 2,000 individual passivated microcrystalline layers in the manner described above, but it is also possible to arrange such ALs one above the other to form so-called multilayers, so that electroluminescence occurs a very high efficiency.
  • a further improvement can be achieved by using insulator layers, e.g. from a-SiC: H or a-SiN: H, as an initiating contact.
  • the charge carriers get into the active layer (AL) through tunnels and reach them with very high energy. This results in a further increase in efficiency.
  • a further improvement in the yield is achieved by repeating the active layers (AL) and insulating layers (IL).
  • 1 schematically shows a CVD reactor for carrying out the CC-CVD process
  • 2 schematically shows the formation of the microcrystalline layer for two selected areas during the process
  • Fig. 7 shows various embodiments of luminescent Si structures.
  • Fig. 1 shows schematically in the upper part of the double graphic the state of the reaction chamber of a CVD reactor for the two process steps.
  • the example concerns the deposition of silicon using SiH 4 as process gas and hydrogen.
  • the reactor 1 is provided with an inlet 2 for the process gas, here SiH 4 , and a separate inlet 3 for the hydrogen.
  • the reactor 1 is connected via the outlet 5 to a pump (not shown).
  • the first step that is to say the deposition of an amorphous SiH layer, is carried out under conditions which are conventional per se with the known process gases SiH 4 and hydrogen.
  • the outlet 5 to the pump is open, so that the deposition on the substrate 6 is carried out in the gas flow.
  • the ordinate shows the pressure in mbar.
  • the conditions for depositing the a-Si: H layer were as follows: - Total gas flow 22 sccm (5 sccm SiH 4 +
  • the deposition rate under these conditions was 2.5 ⁇ / s.
  • a time period of 35 s was selected for the time period (T d ).
  • T d is approximately 5 s. This makes it possible to produce 12.4 ⁇ thick a-Si: H layers in each cycle.
  • the second step of the cycle for producing the microcrystalline layers is essential to the invention.
  • the output 5 to the pump and the feeds 2 and 3 for the process gas stream and the hydrogen are closed for a certain period of time T H.
  • the procedure was such that the interruption of the hydrogen flow (switching point B) was carried out after the interruption of the process gas flow and the closing of the outlet to the pump (switching point A). It is thereby achieved that the pressure in the reactor rises as a result of the inflowing hydrogen, so that the hydrogen treatment is carried out with an increased proportion of hydrogen, which enables acceleration of the second process step.
  • Curve C within the time interval T H shows the pressure curve as it is for CC hydrogen treatment.
  • D represents the course as it occurs when the plasma is switched off or when the process is open, ie in the process known from the prior art. How this difference works is from the lower part of the double graphic.
  • E shows the course for the CC process according to the invention
  • F shows the course for the "open process" known from the prior art.
  • the SiH 4 concentration at the beginning of the second step, ie during the hydrogen treatment is zero (curve F).
  • the hydrogen treatment takes place in a pure hydrogen atmosphere.
  • the hydrogen treatment in the CC-CVD process takes place in the presence of SiH 4 molecules. This fact obviously has a positive effect on the deposition rate.
  • Fig. 2 shows schematically the formation of the microcrystalline layer, starting from the amorphous layer (a) to the microcrystalline layer (b).
  • An amorphous SiH layer is formed by the first process step of the cycle. This amorphous SiH layer contains partially ordered districts (see arrow).
  • the microcrystalline layer forms, starting from the partially ordered areas shown in (a), and this process can be explained in such a way that it takes place in two stages.
  • a first stage is called “nucleation” and a second stage is called “recrystallization”.
  • G and S symbolize the silicon atoms in the gas phase (G) and the SiH species (S).
  • FIG. 3 shows a comparison of the Raman spectra of two samples which were produced by the method according to the invention.
  • the Raman spectrum shows a curve A of sample C 409 that was 15 seconds and a curve B (sample C 407) that was treated with H 2 for 90 seconds and a curve C of sample 0408. From this it can be seen that the invention Process is very flexible with regard to the formation of crystallinity.
  • the Raman intensity is plotted on the ordinate.
  • Fig. 4 shows the increase in conductivity (in S / cm) with the progress of the hydrogen treatment (in s). This is particularly advantageous for microcrystalline TFTs.
  • FIG. 5 shows how the deposition rate ( ⁇ / min) of the method according to the invention (symbolized by filled triangles) compared to the open one Process (filled squares) differs. For completeness, the hydrogen dilution is included in this graphic. The activation energy is plotted on the abscissa.
  • microcrystalline layers produced by the process according to the invention are clearly superior to the prior art. These layers open up possible applications both for luminescence applications and for transistors or solar cells.
  • FIG. 6 (a) to (f) now schematically shows the structure of the microcrystalline layers with (c to f) and without (a to d) passivation.
  • the sequence of figures a, c, e shows the embodiment of the invention in which a microcrystalline layer has been deposited and the individual crystallites are partially spaced apart.
  • the passivation is characterized by a ring around the individual crystallites.
  • an AL is understood to mean both a single microcrystalline layer (c) and 2 to 2,000 microcrystalline layers (e) deposited one above the other.
  • FIGS 6 b, d, f now illustrate the state when an almost closed microcrystalline layer is present.
  • the passivation leads to a passivation layer that lies almost continuously over the individual densely arranged crystallites.
  • FIG. 7 shows the application of the microcrystalline layers described above for luminescence applications.
  • Fig. 7 (a) shows the structure of an SB diode (Schottky barrier diode).
  • SB diode Schottky barrier diode
  • TCO contact electrode layer
  • An AL layer is then applied to such a substrate using the CVD process described above.
  • This AL can consist of 2 to 2,000 individual microcrystalline layers. It is not necessary that every single layer is passivated.
  • an active layer produced in this way is again provided with a contact electrode layer on the surface.
  • the contact electrode layer is n-conducting (n-Si) with a metal contact.
  • the contact electrode layer applied to the substrate in the example according to FIG. 7 (a) consists of ITO (indium tin oxide). Electroluminescence was observed when DC voltage was applied to such an SB diode.
  • FIG. 7 (b) An improvement in the efficiency of electroluminescence can be achieved (FIG. 7 (b)) by applying insulation layers.
  • Fig. 7 (b) shows an example of the construction of such an electroluminescent application.
  • An indium-tin oxide contact electrode (ITO) is applied to the glass substrate as in FIG. 7 (a).
  • the active one Layer AL is surrounded by two insulation layers IL.
  • the thickness of such a layer is in the range of 20 to 500 ⁇ .
  • Such an insulator layer can consist, for example, of amorphous SiC: H or amorphous SiN: H. If an alternating voltage is applied, the charge carriers enter the active layer through tunnels and reach them with high energy. Important parameters for this ac operation are

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Abstract

The invention pertains to a process for producing luminescent elemental structures wherein a microcrystalline film is produced on a substrate and then activated to form an active layer (AL) and then contacted so that a voltage can be applied, the microcrystalline film being made of elements of main group IV of the periodic table, in particular Si, Ge, Sn or their alloys, where CVD is used to produce and passivate a microcrystalline film with a thickness of < 100 Å so as to form an activated layer (AL) which produces electroluminescence when direct voltage is applied. The invention also pertains to luminescent elemental structures thus produced.

Description

Verfahren zum Herstellen von lumineszenten  Process for making luminescent
Elementstrukturen  Element structures
Die Erfindung betrifft ein Verfahren zur Herstellung von lumineszenten Elementstrukturen mittels CVD-Verfahren, wobei mikrokristalline Schichten aus Elementen der IV. HGr abgeschieden und diese in-situ passiviert werden. The invention relates to a method for producing luminescent element structures by means of the CVD method, wherein microcrystalline layers of elements of the IV. HGr are deposited and these are passivated in situ.
Unter Lumineszenz versteht man die Emission von Licht im sichtbaren Bereich, im UV- und IR-Spektralbereich, u.a. von Festkörpern nach Energiezufuhr. Die Lumineszenz ist auf einen Übergang von einem Elektron aus einem energetisch höheren Zustand in einen unbesetzten energetisch tieferen Zustand zurückzuführen. Da unbesetzte Elektronenzustande oft als positiv geladene "Löcher" behandelt werden, läßt sich die Lumineszenz auch als Rekombination eines Elektronenlochpaares beschreiben, bei dem die freiwerdende Energie zumindest teilweise in Form eines Lichtquants (Photons) abgegeben wird. Luminescence is the emission of light in the visible range, in the UV and IR spectral range, including from solids after the supply of energy. The luminescence is due to a transition from an electron from an energetically higher state to an unoccupied energetically lower state. Since unoccupied electron states are often treated as positively charged "holes", luminescence can also be described as a recombination of an electron hole pair in which the energy released is released is at least partially emitted in the form of a light quantum (photon).
Die Lumineszenzprozesse lassen sich nach der Art der Energiezufuhr in Photolumineszenz (optische Anregung) und Elektrolumineszenz (elektrische Anregung durch Anlegen einer Spannung) einteilen. The luminescence processes can be divided into photoluminescence (optical excitation) and electroluminescence (electrical excitation by applying a voltage) according to the type of energy supply.
Dem Phänomen der Lumineszenz kommt bei den halbleitenden Materialien besonderes Interesse zu, da dadurch verschiedene Anwendungen in der Mikroelektronik ermöglicht werden. Lange Zeit ist man davon ausgegangen, daß sich nur Strukturen aus solchen Halbleitermaterialien für eine Lichtemission eignen, die einen direkten Bandübergang aufweisen. Typische Materialien mit einem derartigen direkten Bandübergang sind beispielsweise GaAs-Verbindungshalbleiter. Im Gegensatz dazu ist Silizium ein Halbleitermaterial mit einem indirekten Bandübergang. Es war deshalb zu erwarten, daß Silizium nicht für Elektrolumineszenz-Anwendungen zur Verfügung steht. In jüngster Zeit sind jedoch verschiedene Methoden und Verfahren bekanntgeworden, die es ermöglichen, eine elektrolumineszente Si-Struktur herzustellen. The phenomenon of luminescence is of particular interest in the semiconducting materials, since it enables various applications in microelectronics. For a long time it was assumed that only structures made of such semiconductor materials are suitable for light emission that have a direct band transition. Typical materials with such a direct band transition are, for example, GaAs compound semiconductors. In contrast, silicon is a semiconductor material with an indirect band transition. It was therefore to be expected that silicon would not be available for electroluminescence applications. However, various methods and processes have recently become known which make it possible to produce an electroluminescent Si structure.
Alle diese Arbeiten gehen dabei von Si-Wafern aus, die in einem Flußsäurebad anodisiert werden, um so mikroporöse Si-Strukturen zu realisieren. In der DE-OS 41 26 955 wird ein derartiges Verfahren beschrieben. Die elektrolumineszente Si-Struktur wird dabei in der Art erzeugt, daß während des Anodisierens des Si-Wafers im Säurebad der Si-Wafer auf der anodischen Seite zumindest teilweise über eine bestimmte Zeitspanne belichtet wird. Dadurch sollen Si- Strukturen erhalten werden, die nach weiteren Verfahrensschritten nach Anlegung eines elektrischen Feldes Elektrolumineszenz zeigen. In der US 5,206,523 wird ebenfalls eine mikroporöse Si-Struktur offenbart, die ebenfalls durch eine Säurebehandlung hergestellt wird. Dabei sollen durch ein Anodisieren in einem Flußsäureelektrolyten sogenannten Quantendrähte entstehen, die eine Änderung des energetischen Bandabstandes der mikroporösen Si-Struktur gegenüber einem kristallinen Silizium zur Folge haben. All of this work is based on Si wafers that are anodized in a hydrofluoric acid bath in order to realize microporous Si structures. Such a method is described in DE-OS 41 26 955. The electroluminescent Si structure is produced in such a way that, during the anodizing of the Si wafer in the acid bath, the Si wafer on the anodic side is at least partially exposed for a certain period of time. This should Structures are obtained which show further electroluminescence after the application of an electric field. US Pat. No. 5,206,523 also discloses a microporous Si structure which is also produced by an acid treatment. Anodizing in a hydrofluoric acid electrolyte is said to produce so-called quantum wires, which result in a change in the energy band gap of the microporous Si structure compared to a crystalline silicon.
Alle Verfahren des Standes der Technik gehen demnach davon aus, daß nur dann eine Elektrolumineszenz erreicht wird, wenn Si-Wafer in einem wäßrigen Flußsäurebad zur Erzeugung von mikroporösen Si-Schichten anodisiert werden. Diese Verfahrensweise ist jedoch nicht nur umständlich zu handhaben, sondern sie weist auch noch Nachteile in bezug auf die Strukturierung der Oberfläche und der Schichtdicke auf. Bei den Verfahren des Standes der Technik ist es nämlich nicht möglich, beliebig dicke Si-Schichten mit dem Säurebad zu behandeln. Der Säureprozeß erfordert genau festgelegte Parameter sowohl in bezug auf die Steuerung des Bades als auch auf den Si-Wafer. Dadurch ist es auch nicht möglich, die Lumineszenzwirkung durch besonders dicke Schichten zu steigern. Die Effizienz der mit den Verfahren des Standes der Technik hergestellten Schichten in bezug auf die Elektrolumineszenzwirkung läßt deshalb sehr zu wünschen übrig. Zudem ist man im Gegensatz zu der Verwendung von CVD-Schichten auf den Si-Wafer als Substrat angewiesen. Ausgehend hiervon ist es die Aufgabe der vorliegenden Erfindung ein neues Verfahren zur Verfügung zu stellen, mit dem es möglich ist, lumineszente Elementstrukturen herzustellen, ohne daß dabei eine naßchemische Ätzung erfolgt. Das Verfahren soll einfach und kostengünstig durchführbar sein. All of the prior art processes therefore assume that electroluminescence is only achieved if Si wafers are anodized in an aqueous hydrofluoric acid bath to produce microporous Si layers. However, this procedure is not only difficult to handle, it also has disadvantages with regard to the structuring of the surface and the layer thickness. With the methods of the prior art, it is not possible to treat Si layers of any thickness with the acid bath. The acid process requires well-defined parameters with respect to both the control of the bath and the Si wafer. As a result, it is also not possible to increase the luminescence effect by means of particularly thick layers. The efficiency of the layers produced by the methods of the prior art in relation to the electroluminescent effect therefore leaves much to be desired. In addition, in contrast to the use of CVD layers, one has to rely on the Si wafer as a substrate. Proceeding from this, it is the object of the present invention to provide a new method with which it is possible to produce luminescent element structures without wet chemical etching taking place. The process should be simple and inexpensive to carry out.
Die Aufgabe wird durch die kennzeichnenden Merkmale des Anspruches 1 gelöst. Die Unteransprüche zeigen vorteilhafte Weiterbildungen auf. The object is achieved by the characterizing features of claim 1. The subclaims show advantageous developments.
Erfindungsgemäß wird demnach vorgeschlagen, mikrokristalline Schichten mittels CVD-Verfahren auf einem Substrat abzuscheiden und gleichzeitig in-situ eine Passivierung dieser mikrokristallinen Schichten vorzunehmen. Die dadurch hergestellten aktivierten Accordingly, it is proposed according to the invention to deposit microcrystalline layers on a substrate by means of the CVD method and at the same time to passivate these microcrystalline layers in situ. The activated thereby produced
Schichten (activated layer - AL) dürfen eine Dicke von 100 A nicht überschreiten. Bevorzugt ist es hierbei, wenn die AL im Bereich von 20 bis 50 Å liegt. Layers (activated layer - AL) must not exceed a thickness of 100 A. It is preferred here if the AL is in the range from 20 to 50 Å.
Besonders vorteilhaft beim erfindungsgemäß vorgeschlagenen Verfahren ist nun, daß durch die Erzeugung der mikrokristallinen Schichten mittels der CVD-Methode die mikrokristallinen Schichten selbst in bezug auf ihren Kristallitanteil gesteuert werden können. So ist es einerseits möglich, nahezu geschlossene mikrokristalline Schichten zu erzeugen, wie auch mikrokristalline Schichten herzustellen, bei denen die einzelnen Kristallite zum Teil zueinander beabstandet sind. It is particularly advantageous in the method proposed according to the invention that the microcrystalline layers themselves can be controlled with respect to their crystallite content by generating the microcrystalline layers using the CVD method. On the one hand, it is possible to produce almost closed microcrystalline layers, as well as to produce microcrystalline layers in which the individual crystallites are partially spaced apart.
Wie vorstehend erwähnt, erfolgt die Abscheidung der mikrokristallinen Schichten mittels der CVD-Methode. Aus der Literatur sind hierbei zur Herstellung von mikrokristallinen Silizium-Schichten verschiedene Verfahren bekannt. As mentioned above, the microcrystalline layers are deposited using the CVD method. From the literature are here for the production of microcrystalline silicon layers known various processes.
Die Herstellung der Schichten wird dabei unter Verwendung von SiH4 in Wasserstoff als Prozeßgas vorgenommen. SiH4 wird dabei in stark verdünnter Form in Wasserstoff (weniger als 5 Vol.%) angewandt (T. Hamasaki, H. Kurata, M. Hirose, U. Osaka, Appl. Phys. Lett. 37 (1980) 1084). Die Niedertemperaturbildung der kristallinen Phase kann dabei als Gleichgewicht verstanden werden zwischen der Silizium-Abscheidung und dem Abtragen der Bereiche mit ungeordneten Si-Si-Bindungen durch den atomaren Wasserstoff. Dieser Prozeß wird als Wasserstoff-Ätzen bezeichnet (C.C. Tsai, G.B. Anderson, R. Thompson, B. Wacker, J. Non-Cryst. Sol. 114 (1989) 151). Ein Problem dieser konventionellen PE-CVD ist, daß das Wachstum der geordneten mikrokristallinen Si-Schicht milde Plasmabedingungen erfordert, wohingegen die Produktion des nötigen atomaren Wasserstoffes für das Wasserstoff-Ätzen einen hohen Druck und eine hohe Leistung des Wasserstoffplasmas erfordert. Ein anderes Problem ist, daß die Abscheiderate mit 5 bis 10 Å/min sehr gering ist. Zur Lösung dieses Problems wurden in der Zwischenzeit mehrere zyklische Methoden zur Herstellung von μc-Si:H und verwandten Schichten wie μc-Si:Ge:H vorgeschlagen, die alle eine Trennung in zwei Verfahrensschritte vorsehen. Danach wird in einem ersten The layers are produced using SiH 4 in hydrogen as the process gas. SiH 4 is used in a highly dilute form in hydrogen (less than 5% by volume) (T. Hamasaki, H. Kurata, M. Hirose, U. Osaka, Appl. Phys. Lett. 37 (1980) 1084). The low-temperature formation of the crystalline phase can be understood as an equilibrium between the silicon deposition and the removal of the areas with disordered Si-Si bonds by the atomic hydrogen. This process is referred to as hydrogen etching (CC Tsai, GB Anderson, R. Thompson, B. Wacker, J. Non-Cryst. Sol. 114 (1989) 151). A problem with this conventional PE-CVD is that the growth of the ordered microcrystalline Si layer requires mild plasma conditions, whereas the production of the atomic hydrogen required for the hydrogen etching requires high pressure and high power of the hydrogen plasma. Another problem is that the deposition rate is very low at 5 to 10 Å / min. In the meantime, several cyclical methods for producing μc-Si: H and related layers such as μc-Si: Ge: H have been proposed to solve this problem, all of which provide for a separation into two process steps. After that, in a first
Schritt z.B. eine amorphe SiH-Schicht abgeschieden unter den für die Si-Abscheidung günstigen Bedingungen und dann in einem zweiten Schritt das Wasserstoff-Ätzen unter den für die Wasserstoff-Ätzung erforderlichen Bedingungen vorgenommen (A. Asano, T. Ichimura, H. Sakai, J. Appl. Phys. 65 (1989) 2439. A. Asano, Appl. Phys. Lett. 56 (1990) 533). Die Wasserstoffbehandlung wird dabei in der Weise durchgeführt, daß ein konstanter Wasserstofffluß in den CVD-Reaktor über das Substrat geleitet wird. Step, for example, deposited an amorphous SiH layer under the conditions favorable for the Si deposition and then, in a second step, carried out the hydrogen etching under the conditions required for the hydrogen etching (A. Asano, T. Ichimura, H. Sakai, J. Appl. Phys. 65 (1989) 2439. A. Asano, Appl. Phys. Lett. 56 (1990) 533). The hydrogen treatment is carried out in such a way that a constant hydrogen flow is conducted into the CVD reactor over the substrate.
Die Herstellung derartiger mikrokristalliner Schichten ist aber auch mittels eines sogenannten CC-CVD-Prozesses (closed chamber CVD-Prozeß) möglich. Diese Abscheidemethode entspricht im wesentlichen der vorstehend beschriebenen, jedoch mit dem Unterschied, daß die Wasserstoffbehandlung in einem geschlossenen System durchgeführt wird, wobei dann deutlich höhere Abscheideraten erzielt werden. Die auf diese Weise hergestellten mikrokristallinen Schichten zeichnen sich besonders dadurch aus, daß die mikrokristalline Schicht einen Kristallitanteil von 20 bis 95 % aufweist, wobei sich unter anderem auch sogenannte Element-Dots, d.h. räumlich begrenzte Kristallite, herstellen lassen. The production of such microcrystalline layers is also possible by means of a so-called CC-CVD process (closed chamber CVD process). This deposition method corresponds essentially to that described above, but with the difference that the hydrogen treatment is carried out in a closed system, in which case significantly higher deposition rates are achieved. The microcrystalline layers produced in this way are particularly distinguished by the fact that the microcrystalline layer has a crystallite content of 20 to 95%, among other things also so-called element dots, i.e. spatially limited crystallites.
Erfindungsgemäß wird bei der Wasserstoffbehandlung so vorgegangen, daß nach der Abscheidung der amorphen Schicht mit an sich bekannten Prozeßgasen und unter üblichen Bedingungen der Prozeßgasstrom und der Wasserstoffluß sowie die Verbindung des CVD-Reaktors zur Pumpe zumindest zeitweise unterbrochen werden. Die Wasserstoffbehandlung erfolgt mit der noch im Reaktor befindlichen Menge an Wasserstoff. Bevorzugterweise wird jedoch so vorgegangen, daß der Wasserstofffluß zeitlich verzögert abgeschaltet wird, so daß ein erhöhter Wasserstoffanteil im Reaktor vorhanden ist. Dadurch, daß der Wasserstoff im geschlossenen System vorhanden ist, wird die Umwandlung der amorphen According to the invention, the hydrogen treatment is carried out in such a way that after the deposition of the amorphous layer with process gases known per se and under usual conditions, the process gas flow and the hydrogen flow and the connection of the CVD reactor to the pump are interrupted at least temporarily. The hydrogen treatment is carried out with the amount of hydrogen still in the reactor. However, the procedure is preferably such that the hydrogen flow is switched off with a time delay, so that there is an increased proportion of hydrogen in the reactor. Because the hydrogen is present in the closed system, the conversion of the amorphous
Schicht zur mikrokristallinen Schicht begünstigt. Die Zersetzung von SiH4 in starker Wasserstoffverdünnung im Plasma ist ein reversibler Prozeß, der durch die folgende Beziehung ausgedrückt werden kann: SiHn (plasma) < - - - > Si (solid) + n * H (plasma) Layer favored to the microcrystalline layer. The Decomposition of SiH 4 in strong hydrogen dilution in plasma is a reversible process, which can be expressed by the following relationship: SiH n (plasma) <- - -> Si (solid) + n * H (plasma)
Demnach werden durch die Wasserstoffatome die Siliziumatome aus der amorphen festen Siliziumphase weggeätzt, und es bildet sich ein SiH-Plasma aus. Da der Angriff der Wasserstoffatome an bevorzugten Stellen auf der amorphen Siliziumschicht stattfindet, bilden sich auch entsprechende mikrokristalline Schichten an bevorzugten Stellen aus. Dadurch, daß in einem geschlossenen System gearbeitet wird, ist sichergestellt, daß die sich im Reaktor bildenden SiHx-Gasspezies nicht durch den fortdauernden Wasserstofffluß aus dem System entfernt werden, sondern daß ein quasi stationärer Zustand erreicht wird, so daß eine erhöhte Abscheiderate erzielt werden kann. Bevorzugterweise wird deshalb vorgeschlagen, daß der Wasserstoffanteil erhöht wird, so daß eine Beschleunigung des Ätzens stattfindet und eine nochmals deutlich erhöhte Abscheiderate erzielt wird. Dies wird dadurch erreicht, daß im zweiten Schritt nicht gleichzeitig der Prozeßgasstrom und der Wasserstoffstrom sowie dieAccordingly, the silicon atoms are etched away from the amorphous solid silicon phase by the hydrogen atoms, and an SiH plasma is formed. Since the attack of the hydrogen atoms takes place at preferred locations on the amorphous silicon layer, corresponding microcrystalline layers also form at preferred locations. Working in a closed system ensures that the SiH x gas species that form in the reactor are not removed from the system by the continuous flow of hydrogen, but that a quasi-steady state is achieved, so that an increased deposition rate is achieved can. It is therefore preferably proposed that the proportion of hydrogen be increased so that the etching is accelerated and a further significantly increased deposition rate is achieved. This is achieved in that the process gas stream and the hydrogen stream and the
Verbindung zur Vakuumpumpe unterbrochen werden, sondern daß der Wasserstoffstrom noch kurzzeitig länger in den Reaktor einfließen kann, maximal so lange, bis eine Druckerhöhung im Reaktor bis etwa 1 Atmosphäre stattfindet. Das Verfahren bietet den weiteren Vorteil, daß durch die Dauer der Wasserstoffbehandlung der Kristallitanteil individuell gesteuert werden kann. Der Kristallitanteil, der mit dem erfindungsgemäßen Verfahren erreicht werden kann, liegt maximal bei 95 %. Durch die Wahl der Prozeßparameter läßt sich zudem die Kristallitgröße einstellen. Connection to the vacuum pump are interrupted, but that the hydrogen stream can flow into the reactor for a short time, at most until an increase in pressure in the reactor to about 1 atmosphere takes place. The process offers the further advantage that the crystallite content can be controlled individually by the duration of the hydrogen treatment. The crystallite content that can be achieved with the method according to the invention is at a maximum at 95%. The crystallite size can also be set by selecting the process parameters.
Der vorstehend beschriebene Prozeß wird als CC-CVD-Prozeß bezeichnet. Der zyklische CC-CVD-Prozeß besteht demnach aus einem wiederholbaren Zyklus, wobei jeder Zyklus aus zwei Schritten besteht, nämlich a) der Abscheidung einer dünnen amorphen Siliziumschicht und The process described above is called the CC-CVD process. The cyclic CC-CVD process therefore consists of a repeatable cycle, each cycle consisting of two steps, namely a) the deposition of a thin amorphous silicon layer and
b) einer Wasserstoffbehandlung in einem geschlossenen CVD-Prozeß, wie vorstehend beschrieben. b) hydrogen treatment in a closed CVD process as described above.
Vorteilhaft bei dem erfindungsgemäßen Verfahren ist, daß mehrere Zyklen in einem Prozeß hintereinander durchgeführt werden können. Je nach der gewünschten Schichtdicke können somit 2 bis 2000 Zyklen durchgeführt werden, so daß eine entsprechende Schicht realisiert werden kann. Das vorgestellte Verfahren ist grundsätzlich mit allen gängigen CVD-Verfahren ausführbar. Hierzu zählen ECR-CVD-, VHF-CVD- und Heißdraht-CVD-Prozesse. Es ist auch möglich, bei den einzelnen Schritten jedes Zyklus unterschiedliche CVD-Verfahren einzusetzen. An advantage of the method according to the invention is that several cycles can be carried out in succession in one process. Depending on the desired layer thickness, 2 to 2000 cycles can thus be carried out, so that a corresponding layer can be realized. The method presented can basically be carried out with all common CVD methods. These include ECR-CVD, VHF-CVD and hot wire CVD processes. It is also possible to use different CVD processes for the individual steps of each cycle.
Bevorzugt ist es, wenn das erfindungsgemäße Verfahren mit Silizium als Element und SiH4 und Wasserstoff als Prozeßgase durchgeführt wird. Erfindungswesentlich beim vorgeschlagenen Verfahren ist nun, daß nach Herstellung der mikrokristallinen Schicht, so wie vorstehend beschrieben, entweder im offenen oder im geschlossenen CVD-Prozeß in-situ eine Passivierung dieser mikrokristallinen Schicht erfolgt. Hierfür werden zwei Varianten vorgeschlagen. Zum einen kann die Passivierung mit oxidierenden und/oder nitrierenden Gasen, wie z.B. plasma-akti- viertem N20 oder Sauerstoff erfolgen, andererseits kann die Passivierung aber auch durch Abscheidung einer Passivierungsschicht durchgeführt werden. Für den Fall, daß eine Passivierung mit der Abscheidung einer Passivierungsschicht vorgenommen wird, hat die Passivierungsschicht eine Dicke von 10 bis 100 Å und besteht vorzugsweise aus SiOx oder SiNx. Die Passivierung wird, wie vorstehend bereits erläutert, in- situ, d.h. in der CVD-Anlage, direkt nach Abscheiden der Schicht vorgenommen. Dadurch wird nämlich eine besonders einfache und kostengünstige Verfahrensweise zur Herstellung der lumineszenten Elementstrukturen ermöglicht. Sowohl die Abscheidung wie auch die Passivierung wird demnach mit einer CVD-Anlage in einem Prozeßschritt möglich. It is preferred if the method according to the invention is carried out with silicon as element and SiH 4 and hydrogen as process gases. It is essential to the invention in the proposed method that after the production of the microcrystalline layer, as described above, this microcrystalline layer is passivated in situ either in the open or in the closed CVD process. Two variants are proposed for this. On the one hand, the passivation can be carried out using oxidizing and / or nitriding gases, such as, for example, plasma-activated N 2 O or oxygen, on the other hand the passivation can also be carried out by depositing a passivation layer. In the event that passivation is carried out with the deposition of a passivation layer, the passivation layer has a thickness of 10 to 100 Å and preferably consists of SiO x or SiN x . As already explained above, the passivation is carried out in situ, ie in the CVD system, directly after the layer has been deposited. This enables a particularly simple and inexpensive procedure for producing the luminescent element structures. Both the deposition and the passivation are therefore possible with a CVD system in one process step.
Wie eingangs bereits geschildert, wird erfindungsgemaß durch Abscheiden einer mikrokristallinen Schicht und anschließender Passivierung eine sogenannte activated layer (AL) gebildet. Erfindungsgemäß ist es nun besonders bevorzugt, daß diese AL nicht aus einer passivierten Schicht, sondern aus 2 bis 2.000, bevorzugt bis 200, übereinander abgeschiedenen mikrokristallinen und passivierten Schichten besteht. Erfindungsgemäß wird demnach unter einer AI sowohl eine einzige mikrokristalline Schicht verstanden, die passiviert ist, wie auch 2 bis 2.000 übereinander abgeschiedene mikrokristalline und passivierte Schichten, die dann gemeinsam die AL bilden. As already described at the beginning, a so-called activated layer (AL) is formed according to the invention by depositing a microcrystalline layer and subsequent passivation. According to the invention, it is now particularly preferred that this AL does not consist of a passivated layer, but of 2 to 2,000, preferably up to 200, microcrystalline and passivated layers deposited on top of one another. According to the invention, AI is understood to mean both a single microcrystalline layer that is passivated and 2 to 2,000 microcrystalline and passivated layers deposited one above the other, which then together form the AL.
Die Erfindung schließt selbstverständlich auch AL-Schichten mit ein, die aus 2 bis 2.000 nebeneinander angeordneten mikrokristallinen Schichten besteht, wobei nicht notwendigerweise jede Schicht passiviert sein muß. Es kann z.B. nur jede zweite Schicht passiviert sein, ohne daß eine relevante Beeinträchtigung der Lumineszenz erfolgt. The invention naturally also includes AL layers which consist of 2 to 2,000 microcrystalline layers arranged next to one another, each layer does not necessarily have to be passivated. For example, only every second layer can be passivated without any relevant impairment of the luminescence.
Das erfindungsgemäße Verfahren bietet aber noch weitere Vorteile. So ist es nicht nur möglich, mittels des CVD-Prozesses in der vorstehend beschriebenen Weise eine AL, bestehend aus 2 bis 2.000 einzelnen passivierten mikrokristallinen Schichten herzustellen, sondern es können auch derartige AL übereinander zu sogenannten Multischichten angeordnet werden, so daß sich eine Elektrolumineszenz mit einer sehr hohen Effizienz erzielen läßt. However, the method according to the invention offers further advantages. It is not only possible to use the CVD process to produce an AL consisting of 2 to 2,000 individual passivated microcrystalline layers in the manner described above, but it is also possible to arrange such ALs one above the other to form so-called multilayers, so that electroluminescence occurs a very high efficiency.
Eine weitere Verbesserung läßt sich durch die Verwendung von Isolatorschichten, z.B. aus a-SiC:H oder a-SiN:H, als initiierenden Kontakt erreichen. Die Ladungsträger gelangen dabei durch Tunneln in die akti- ve Schicht (AL) und erreichen sie mit sehr hoher Energie. Dadurch wird eine erneute Steigerung der Effizienz erreicht. Eine weitere Verbesserung der Ausbeute wird durch die Wiederholung der aktiven Schichten (AL) und isolierenden Schichten (IL) erreicht. A further improvement can be achieved by using insulator layers, e.g. from a-SiC: H or a-SiN: H, as an initiating contact. The charge carriers get into the active layer (AL) through tunnels and reach them with very high energy. This results in a further increase in efficiency. A further improvement in the yield is achieved by repeating the active layers (AL) and insulating layers (IL).
Weitere Merkmale, Einzelheiten und Vorzüge der Erfindung ergeben sich aus der folgenden Beschreibung eines Verfahrensbeispieles der Erfindung sowie anhand der Zeichnungen. Es zeigen: Further features, details and advantages of the invention will become apparent from the following description of a process example of the invention and from the drawings. Show it:
Fig. 1 schematisch einen CVD-Reaktor zur Durchführung des CC-CVD-Prozesses, Fig. 2 schematisch für zwei ausgewählte Bereiche während des Verfahrens die Bildung der mikrokristallinen Schicht, 1 schematically shows a CVD reactor for carrying out the CC-CVD process, 2 schematically shows the formation of the microcrystalline layer for two selected areas during the process,
Fig. 3 Raman-Spektren einer amorphen (A) und zwei- er mikrokristalliner Schichten  3 Raman spectra of an amorphous (A) and two microcrystalline layers
(B, C),  (B, C),
Fig. 4 die Leitfähigkeit der erfindungsgemäß hergestellten Schicht,  4 shows the conductivity of the layer produced according to the invention,
Fig. 5 die Abscheiderate,  5 shows the deposition rate,
Fig. 6 zeigt einzelne mikrokristalline Schichten mit und ohne Passivierung, 6 shows individual microcrystalline layers with and without passivation,
Fig. 7 verschiedene Ausführungsformen von lumineszenten Si-Strukturen. Fig. 1 zeigt im oberen Teil der Doppelgrafik schematisch den Zustand der Reaktionskammer eines CVD-Reaktors für die beiden Verfahrensschritte. Das Beispiel betrifft die Abscheidung von Silizium mittels SiH4 als Prozeßgas und Wasserstoff. 7 shows various embodiments of luminescent Si structures. Fig. 1 shows schematically in the upper part of the double graphic the state of the reaction chamber of a CVD reactor for the two process steps. The example concerns the deposition of silicon using SiH 4 as process gas and hydrogen.
Der Reaktor 1 ist mit einem Zugang 2 für das Prozeßgas, hier SiH4, und einem separaten Zugang 3 für den Wasserstoff versehen. Der Reaktor 1 ist dabei über den Ausgang 5 mit einer Pumpe (nicht abgebildet) verbunden. Der erste Schritt, d.h. die Abscheidung einer amorphen SiH-Schicht, wird unter an und für sich üblichen Bedingungen mit den bekannten Prozeßgasen SiH4 und Wasserstoff durchgeführt. Der Ausgang 5 zur Pumpe ist offen, so daß die Abscheidung auf dem Substrat 6 im Gasfluß vorgenommen wird. Aus der Ordinate ist der Druck in mbar ersichtlich. Die Bedingungen zur Abscheidung der a-Si:H-Schicht waren wie folgt: - Gesamtgasfluß 22 sccm (5 sccm SiH4 + The reactor 1 is provided with an inlet 2 for the process gas, here SiH 4 , and a separate inlet 3 for the hydrogen. The reactor 1 is connected via the outlet 5 to a pump (not shown). The first step, that is to say the deposition of an amorphous SiH layer, is carried out under conditions which are conventional per se with the known process gases SiH 4 and hydrogen. The outlet 5 to the pump is open, so that the deposition on the substrate 6 is carried out in the gas flow. The ordinate shows the pressure in mbar. The conditions for depositing the a-Si: H layer were as follows: - Total gas flow 22 sccm (5 sccm SiH 4 +
17 sccm H2), 17 sccm H 2 ),
- Gasdruck 0,15 mbar, - gas pressure 0.15 mbar,
- Leistung 0,2 W/cm2, - power 0.2 W / cm 2 ,
- Substrattemperatur 270° C. - substrate temperature 270 ° C.
Die Abscheiderate betrug unter diesen Bedingungen 2,5 Å/s. Zur besseren Übersicht des Verfahrensablaufes wurde für die Zeitspanne (Td) eine Zeitspanne von 35 s gewählt. Es ist aber ausreichend, wenn Td ungefähr 5 s beträgt. Damit ist es möglich, 12,4 Å dicke a-Si:H-Schichten in jedem Zyklus zu erzeugen. The deposition rate under these conditions was 2.5 Å / s. For a better overview of the process sequence, a time period of 35 s was selected for the time period (T d ). However, it is sufficient if T d is approximately 5 s. This makes it possible to produce 12.4 Å thick a-Si: H layers in each cycle.
Erfindungswesentlich ist der zweite Schritt des Zyklus zur Erzeugung der mikrokristallinen Schichten. Dazu werden der Ausgang 5 zur Pumpe sowie die Zuführungen 2 und 3 für den Prozeßgasstrom und den Wasserstoff für eine bestimmte Zeitspanne TH geschlossen. Im Beispielsfall ist so vorgegangen worden, daß die Unterbrechung des Wasserstoffflusses (Schaltpunkt B) zeitlich nach der Unterbrechung des Prozeßgasstromes und der Schließung des Ausganges zur Pumpe (Schaltpunkt A) vorgenommen wurde. Dadurch wird erreicht, daß durch den nachströmenden Wasserstoff der Druck im Reaktor ansteigt, so daß die Wasserstoffbehandlung mit einem erhöhten Wasserstoffanteil durchgeführt wird, wodurch eine Beschleunigung des zweiten Verfahrensschrittes ermöglicht wird. Die Kurve C innerhalb des Zeitintervalles TH gibt dabei den Druckverlauf wieder, wie er bei der CC-Wasserstoffbehandlung vorliegt. D gibt dabei den Verlauf wieder, wie er bei abgeschaltetem Plasma oder beim offenen, d.h. bei dem aus dem Stand der Technik bekannten Prozeß erfolgt. Wie sich dieser Unterschied auswirkt, ist aus dem unteren Teil der Doppelgrafik ersichtlich. E zeigt dabei den Verlauf für den erfindungsgemäßen CC-Prozeß, und F den Verlauf bei dem aus dem Stand der Technik bekannten "offenen Verfahren". Dadurch wird deutlich (schraffierter Bereich), daß während des CC-Prozesses im Gegensatz zum offenen Prozeß noch SiH4-Moleküle im Gasraum vorhanden sind. Bei einem konventionellen zyklischen Prozeß liegt die SiH4-Konzentra- tion bei Beginn des zweiten Schrittes, d.h. bei der Wasserstoffbehandlung, bei Null (Kurve F). In diesem Fall findet demnach die Wasserstoffbehandlung in einer reinen Wasserstoffatmosphäre statt. Im Gegensatz dazu erfolgt die Wasserstoffbehandlung im CC-CVD-Prozeß in Anwesenheit von SiH4-Molekülen. Dieser Umstand wirkt sich offensichtlich positiv auf die Abscheiderate aus. The second step of the cycle for producing the microcrystalline layers is essential to the invention. For this purpose, the output 5 to the pump and the feeds 2 and 3 for the process gas stream and the hydrogen are closed for a certain period of time T H. In the example case, the procedure was such that the interruption of the hydrogen flow (switching point B) was carried out after the interruption of the process gas flow and the closing of the outlet to the pump (switching point A). It is thereby achieved that the pressure in the reactor rises as a result of the inflowing hydrogen, so that the hydrogen treatment is carried out with an increased proportion of hydrogen, which enables acceleration of the second process step. Curve C within the time interval T H shows the pressure curve as it is for CC hydrogen treatment. D represents the course as it occurs when the plasma is switched off or when the process is open, ie in the process known from the prior art. How this difference works is from the lower part of the double graphic. E shows the course for the CC process according to the invention, and F shows the course for the "open process" known from the prior art. This makes it clear (hatched area) that SiH 4 molecules are still present in the gas space during the CC process, in contrast to the open process. In a conventional cyclic process, the SiH 4 concentration at the beginning of the second step, ie during the hydrogen treatment, is zero (curve F). In this case, the hydrogen treatment takes place in a pure hydrogen atmosphere. In contrast, the hydrogen treatment in the CC-CVD process takes place in the presence of SiH 4 molecules. This fact obviously has a positive effect on the deposition rate.
Zur Verdeutlichung des Prozesses wurden verschiedene Proben während des ersten und zweiten Zyklus (a bis e und i) untersucht. Diese Ergebnisse wurden Proben, die in einem offenen Prozeß hergestellt wurden (f bis h), gegenübergestellt (Tabelle 1). Darin bedeuten TH die Zeitdauer der Wasserstoffbehandlung, Δd die To clarify the process, various samples were examined during the first and second cycle (a to e and i). These results were compared to samples which were produced in an open process (f to h) (Table 1). Therein, T H is the duration of the hydrogen treatment, Δd is the
Schichtdicke pro Zyklus, R die Abscheiderate, d die gesamte Filmdicke, σd die Dunkel- und σph die Photoleitfähigkeit sowie Eact die Aktivierungsenergie. Damit wird deutlich, daß mit dem erfindungsgemäßen Verfahren Abscheideraten erzielt werden, die um den Faktor 5 höher sind, als sie mit den bisher üblichen Methoden realisierbar sind. Es werden zudem Leitfähigkeiten erreicht, die um mehrere 10er Potenzen besser als der Stand der Technik sind. Fig. 2 zeigt schematisch die Bildung der mikrokristallinen Schicht, ausgehend von der amorphen Schicht (a) zur mikrokristallinen Schicht (b). Durch den ersten Verfahrensschritt des Zyklus wird eine amorphe SiH-Schicht gebildet. Diese amorphe SiH-Schicht enthält teilweise geordnete Bezirke (siehe Pfeil). Layer thickness per cycle, R the deposition rate, d the total film thickness, σ d the dark and σ ph the photoconductivity and E act the activation energy. This makes it clear that the method according to the invention achieves deposition rates which are 5 times higher than can be achieved with the methods customary hitherto. Conductivities are also achieved which are several powers of ten better than the prior art. Fig. 2 shows schematically the formation of the microcrystalline layer, starting from the amorphous layer (a) to the microcrystalline layer (b). An amorphous SiH layer is formed by the first process step of the cycle. This amorphous SiH layer contains partially ordered districts (see arrow).
Bei der folgenden Wasserstoffbehandlung im geschlossenen System (b) bildet sich - ausgehend von den in (a) aufgezeigten teilweise geordneten Bereichen - die mikrokristalline Schicht aus, wobei dieser Vorgang so erklärt werden kann, daß er in zwei Stufen abläuft. Eine erste Stufe wird hierbei als "nucleation" und eine zweite Stufe als "recrystallization" bezeichnet. G und S symbolisieren dabei die Siliziumatome in der Gasphase (G) und die SiH-Spezies (S). In the subsequent hydrogen treatment in the closed system (b), the microcrystalline layer forms, starting from the partially ordered areas shown in (a), and this process can be explained in such a way that it takes place in two stages. A first stage is called "nucleation" and a second stage is called "recrystallization". G and S symbolize the silicon atoms in the gas phase (G) and the SiH species (S).
Fig. 3 zeigt im Vergleich die Raman-Spektren von zwei Proben, die nach dem erfindungsgemäßen Verfahren her- gestellt wurden. Das Raman-Spektrum zeigt eine Kurve A der Probe C 409, die 15 sec, und eine Kurve B (Probe C 407), die 90 sec mit H2 behandelt wurde sowie eine Kurve C der Probe 0408. Daraus ist ersichtlich, daß das erfindungsgemäße Verfahren in bezug auf die Bildung der Kristallität sehr flexibel ist. Auf der Ordinate ist dabei die Ramanintensität aufgetragen. 3 shows a comparison of the Raman spectra of two samples which were produced by the method according to the invention. The Raman spectrum shows a curve A of sample C 409 that was 15 seconds and a curve B (sample C 407) that was treated with H 2 for 90 seconds and a curve C of sample 0408. From this it can be seen that the invention Process is very flexible with regard to the formation of crystallinity. The Raman intensity is plotted on the ordinate.
Fig. 4 zeigt die Erhöhung der Leitfähigkeit (in S/cm) mit dem Fortschreiten der Wasserstoffbehandlung (in s). Dies ist besonders vorteilhaft für mikrokristalline TFTs. Fig. 4 shows the increase in conductivity (in S / cm) with the progress of the hydrogen treatment (in s). This is particularly advantageous for microcrystalline TFTs.
Fig. 5 macht deutlich, wie sich die Abscheiderate (Å/min) des erfindungsgemäßen Verfahrens (symbolisiert durch gefüllte Dreiecke) gegenüber dem offenen Prozeß (gefüllte Vierecke) unterscheidet. Zur Vollständigkeit ist in dieser Grafik die Wasserstoffverdünnung mit aufgenommen. Auf der Abzisse ist die Aktivierungsenergie aufgetragen. FIG. 5 shows how the deposition rate (Å / min) of the method according to the invention (symbolized by filled triangles) compared to the open one Process (filled squares) differs. For completeness, the hydrogen dilution is included in this graphic. The activation energy is plotted on the abscissa.
Diese Ergebnisse zeigen, daß die mit dem erfindungsgemäßen Verfahren hergestellten mikrokristallinen Schichten gegenüber dem Stand der Technik deutlich überlegen sind. Mit diesen Schichten erschließen sich Anwendungsmöglichkeiten sowohl für Lumineszenzanwendungen als auch für Transistoren oder Solarzellen. These results show that the microcrystalline layers produced by the process according to the invention are clearly superior to the prior art. These layers open up possible applications both for luminescence applications and for transistors or solar cells.
Fig. 6 (a) bis (f) zeigt nun schematisch den Aufbau der mikrokristallinen Schichten mit (c bis f) und ohne (a bis d) Passivierung. Die Figurenfolge a, c, e zeigt die Ausführungsform der Erfindung, bei der eine mikrokristalline Schicht abgeschieden wurde und die einzelnen Kristallite zum Teil beabstandet sind. Die Passivierung ist dabei durch einen Ring um die einzelnen Kristallite gekennzeichnet. Erfindungsgemäß wird hierbei unter einer AL sowohl eine einzelne mikrokristalline Schicht (c), wie auch 2 bis 2.000 übereinander abgeschiedene mikrokristalline Schichten (e) verstanden. 6 (a) to (f) now schematically shows the structure of the microcrystalline layers with (c to f) and without (a to d) passivation. The sequence of figures a, c, e shows the embodiment of the invention in which a microcrystalline layer has been deposited and the individual crystallites are partially spaced apart. The passivation is characterized by a ring around the individual crystallites. According to the invention, an AL is understood to mean both a single microcrystalline layer (c) and 2 to 2,000 microcrystalline layers (e) deposited one above the other.
Die Figuren 6 b, d, f verdeutlichen nun den Zustand bei Vorliegen einer nahezu geschlossenen mikrokristallinen Schicht. In diesem Fall führt dann die Passivierung zu einer Passivierungsschicht, die nahezu durchgängig über den einzelnen dicht angeordneten Kristalliten liegt. Figures 6 b, d, f now illustrate the state when an almost closed microcrystalline layer is present. In this case, the passivation leads to a passivation layer that lies almost continuously over the individual densely arranged crystallites.
Wie bereits vorstehend erwähnt, ist es nicht zwingend erforderlich, einzelne mikrokristalline Schichten (Figur e bzw. f) zu passivieren. Fig. 7 zeigt die Anwendung der vorstehend beschriebenen mikrokristallinen Schichten für Lumineszenzanwendungen. Fig. 7 (a) zeigt den Aufbau einer SB-Diode (Schottky-Barrieren-Diode). Zur Herstellung dieser SB-Diode wird so vorgegangen, daß ein Substrat, bevorzugt Glas oder andere zumindest teilweise lichtdurchlässige Substrate mit einer Kontaktelektrodenschicht (TCO, transparent conducting oxid) versehen werden. Auf ein derartiges Substrat wird dann mittels des vorstehend beschriebenen CVD-Prozesses eine AL-Schicht aufgebracht. Diese AL kann dabei aus 2 bis 2.000 einzelnen mikrokristallinen Schichten bestehen. Es ist hierbei nicht nötig, daß zwingend jede einzelne Schicht passiviert ist. As already mentioned above, it is not absolutely necessary to passivate individual microcrystalline layers (FIGS. E and f). 7 shows the application of the microcrystalline layers described above for luminescence applications. Fig. 7 (a) shows the structure of an SB diode (Schottky barrier diode). To produce this SB diode, the procedure is such that a substrate, preferably glass or other at least partially transparent substrates, is provided with a contact electrode layer (TCO, transparent conducting oxide). An AL layer is then applied to such a substrate using the CVD process described above. This AL can consist of 2 to 2,000 individual microcrystalline layers. It is not necessary that every single layer is passivated.
Eine so hergestellte aktive Schicht wird, um Lumineszenzanwendungen zu realisieren, an der Oberfläche wieder mit einer Kontaktelektrodenschicht versehen.In order to implement luminescence applications, an active layer produced in this way is again provided with a contact electrode layer on the surface.
Im Beispielsfall (Fig. 7 (a)) ist die Kontaktelektrodenschicht n-leitend (n-Si) mit einem MetalIkontakt. Die auf dem Substrat aufgebrachte Kontaktelektrodenschicht besteht im Beispielsfall nach Fig. 7 (a) aus ITO (Indium-Zinnoxid). Bei Anlegung von Gleichspannung an eine derartige SB-Diode konnte Elektrolumineszenz beobachtet werden. In the example case (FIG. 7 (a)), the contact electrode layer is n-conducting (n-Si) with a metal contact. The contact electrode layer applied to the substrate in the example according to FIG. 7 (a) consists of ITO (indium tin oxide). Electroluminescence was observed when DC voltage was applied to such an SB diode.
Eine Verbesserung der Effizienz der Elektrolumineszenz läßt sich dadurch erreichen (Fig. 7 (b)), daß Isolationsschichten aufgebracht werden. Fig. 7 (b) zeigt einen Beispielsfall für den Aufbau einer derartigen Elektrolumineszenzanwendung. Auf dem Glassubstrat ist dabei wie in Fig. 7 (a) eine Indium-Zinnoxid-Kontaktelektrode (ITO) aufgebracht. Die aktive Schicht AL ist jedoch von zwei Isolationsschichten IL umgeben. Die Dicke einer derartigen Schicht liegt im Bereich von 20 bis 500 Å. Eine derartige Isolatorschicht kann z.B. aus amorphem SiC:H oder amorphem SiN:H bestehen. Wird eine Wechselspannung angelegt, so gelangen die Ladungsträger durch Tunneln in die aktive Schicht und erreichen sie mit hoher Energie. Wichtige Parameter für diesen ac-Betrieb sind An improvement in the efficiency of electroluminescence can be achieved (FIG. 7 (b)) by applying insulation layers. Fig. 7 (b) shows an example of the construction of such an electroluminescent application. An indium-tin oxide contact electrode (ITO) is applied to the glass substrate as in FIG. 7 (a). The active one Layer AL, however, is surrounded by two insulation layers IL. The thickness of such a layer is in the range of 20 to 500 Å. Such an insulator layer can consist, for example, of amorphous SiC: H or amorphous SiN: H. If an alternating voltage is applied, the charge carriers enter the active layer through tunnels and reach them with high energy. Important parameters for this ac operation are
a Spannung (bestimmt durch die Dicke und Zusammensetzung der Isolatorschicht) und a voltage (determined by the thickness and composition of the insulator layer) and
b Frequenz (bestimmt durch die Transporteigenschaften und die Zustandsdichte des aktiven Materials. Die Elektrolumineszenz bei einem derartigen Aufbau zeigt eine deutlich bessere Effizienz als die SB-Diode nach Fig. 7 (a). b Frequency (determined by the transport properties and the density of states of the active material. The electroluminescence with such a structure shows a significantly better efficiency than the SB diode according to FIG. 7 (a).
Eine nochmalige Steigerung läßt sich durch sogenannte Multischichten (Fig. 7 (c)) erreichen. Bei einem derartigen Aufbau wird durch die Wiederholung der aktiven und isolierenden Schicht eine nochmalige deutliche Steigerung der Ausbeute erreicht. Die Betriebsspannung erhöht sich entsprechend. A further increase can be achieved by so-called multi-layers (Fig. 7 (c)). With such a construction, the repetition of the active and insulating layer achieves a further significant increase in the yield. The operating voltage increases accordingly.
Figure imgf000020_0001
Figure imgf000020_0001

Claims

Patentansprüche claims
1. Verfahren zum Herstellen von lumineszenten Ele- mentstrukturen, bei dem auf einem Substrat eine mikrokristalline Schicht hergestellt und diese anschließend zu einer aktiven Schicht (AL) aktiviert und dann kontaktiert wird, so daß eine Spannung anlegbar ist, wobei die mikrokristalli- ne Schicht aus Elementen der IV. HGr, insbesondere Si, Ge, Sn oder deren Legierungen, wie SiCXI, GeOx oder SiOxNy besteht, 1. A method for producing luminescent element structures, in which a microcrystalline layer is produced on a substrate and this is subsequently activated to form an active layer (AL) and then contacted, so that a voltage can be applied, the microcrystalline layer being made of Elements of IV. HGr, in particular Si, Ge, Sn or their alloys, such as SiC XI , GeO x or S i O x N y ,
dadurch g e k e n n z e i c h n e t , daß mittels CVD a) eine mikrokristalline Schicht mit einer  by means of the fact that a microcrystalline layer with a
Schichtdicke < 100 Å hergestellt und b) passiviert wird, so daß eine aktivierte  Layer thickness <100 Å is produced and b) passivated, so that an activated
Schicht (AL) entsteht.  Layer (AL) is created.
2. Verfahren nach Anspruch 1, 2. The method according to claim 1,
dadurch gekennzeichnet, daß die Schichtdicke im Bereich von 20 bis 50 Å liegt.  characterized in that the layer thickness is in the range of 20 to 50 Å.
3. Verfahren nach Anspruch 1 oder 2, 3. The method according to claim 1 or 2,
dadurch gekennzeichnet, daß eine mikrokristalline Schicht abgeschieden wird, bei der die einzelnen Kristallite dicht nebeneinander liegen, so daß eine nahezu geschlossene mikrokristalline characterized in that a microcrystalline layer is deposited in which the individual crystallites lie close together, so that an almost closed microcrystalline
Schicht entsteht. Layer arises.
4. Verfahren nach Anspruch 1 oder 2, 4. The method according to claim 1 or 2,
dadurch gekennzeichnet, daß eine mikrokristalline Schicht abgeschieden wird, bei der die Kri stallite zum Teil beabstandet sind, so daß eine unterbrochene mikrokristalline Schicht entsteht. characterized in that a microcrystalline layer is deposited in which the crystal stallites are partially spaced so that an interrupted microcrystalline layer is formed.
5. Verfahren nach mindestens einem der Ansprüche 1 bis 4, 5. The method according to at least one of claims 1 to 4,
dadurch gekennzeichnet, daß die Passivierung mit oxidierenden und/oder nitrierenden Gasen erfolgt.  characterized in that the passivation takes place with oxidizing and / or nitriding gases.
6. Verfahren nach Anspruch 5, 6. The method according to claim 5,
dadurch gekennzeichnet, daß als Gase plasma-aktiviertes N2O oder O2 eingesetzt werden. characterized in that plasma-activated N 2 O or O 2 are used as gases.
7. Verfahren nach mindestens einem der Ansprüche 1 bis 4, 7. The method according to at least one of claims 1 to 4,
dadurch gekennzeichnet, daß die Passivierung durch Deposition einer 10 bis 100 Å dicken passivierenden Schicht erfolgt.  characterized in that the passivation takes place by deposition of a 10 to 100 Å thick passivating layer.
8. Verfahren nach Anspruch 7, 8. The method according to claim 7,
dadurch gekennzeichnet, daß als passivierende Schicht SiOx oder SiNx eingesetzt wird. characterized in that SiO x or SiN x is used as the passivating layer.
9. Verfahren nach mindestens einem der Ansprüche 1 bis 8, 9. The method according to at least one of claims 1 to 8,
dadurch gekennzeichnet, daß eine AL-Schicht gebildet wird, die durch Abscheiden von 2 bis 2.000 passivierten mikrokristallinen Schichten übereinander entsteht.  characterized in that an AL layer is formed which is formed by depositing 2 to 2,000 passivated microcrystalline layers on top of one another.
10. Verfahren nach mindestens einem der Ansprüche 1 bis 9, 10. The method according to at least one of claims 1 to 9,
dadurch gekennzeichnet, daß zwischen dem Substrat und der AL-Schicht eine Isolationsschicht (IL) aufgebracht wird. characterized in that an insulation layer (IL) is applied between the substrate and the AL layer.
11. Verfahren nach mindestens einem der Ansprüche 1 bis 10, 11. The method according to at least one of claims 1 to 10,
dadurch gekennzeichnet, daß auf der dem Substrat gegenüberliegenden Seite der AL-Schicht eine Isolationsschicht (IL) aufgebracht wird.  characterized in that an insulation layer (IL) is applied to the side of the AL layer opposite the substrate.
12. Verfahren nach mindestens einem der Ansprüche 1 bis 11, 12. The method according to at least one of claims 1 to 11,
dadurch gekennzeichnet, daß eine Multischicht in der Weise hergestellt wird, daß 2 bis 50 AL- Schichten übereinander abgeschieden werden.  characterized in that a multilayer is produced in such a way that 2 to 50 AL layers are deposited one above the other.
13. Verfahren nach Anspruch 12, 13. The method according to claim 12,
dadurch gekennzeichnet, daß zwischen den AL- Schichten und/oder nach der letzten AL-Schicht eine Isolationsschicht (IL) aufgebracht wird.  characterized in that an insulation layer (IL) is applied between the AL layers and / or after the last AL layer.
14. Verfahren nach mindestens einem der Ansprüche 1 bis 13, 14. The method according to at least one of claims 1 to 13,
dadurch gekennzeichnet, daß die Kontaktelektrodenschicht ein Metall oder ein TCO (transparent conducting oxid) ist.  characterized in that the contact electrode layer is a metal or a TCO (transparent conducting oxide).
15. Verfahren nach Anspruch 14, 15. The method according to claim 14,
dadurch gekennzeichnet, daß mindestens eine Kontaktelektrodenschicht n-leitend ist.  characterized in that at least one contact electrode layer is n-conductive.
16. Verfahren nach mindestens einem der Ansprüche 1 bis 15, 16. The method according to at least one of claims 1 to 15,
dadurch gekennzeichnet, daß eine mikrokristalline Si-Schicht erzeugt wird. characterized in that a microcrystalline Si layer is produced.
17. Lumineszente Elementstrukturen, 17. Luminescent element structures,
dadurch gekennzeichnet, daß sie nach mindestens einem der Verfahrensansprüche 1 bis 16 hergestellt sind.  characterized in that they are produced according to at least one of the method claims 1 to 16.
PCT/DE1994/001168 1993-09-30 1994-09-30 Process for producing luminescent elemental structures WO1995009443A1 (en)

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EP0721656A1 (en) 1996-07-17
DE4345229A1 (en) 1995-04-06
US5851904A (en) 1998-12-22
JPH09508236A (en) 1997-08-19
DE4345229C2 (en) 1998-04-09
WO1995009435A1 (en) 1995-04-06

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